Endpoint URL for DynamoDB inside localstack's Lambda function - aws-lambda

Question

I'm using localstack for local development. I have a DynamoDB table named readings and I'd like to insert items from a lambda function.
I have deployed simple lambda function in python runtime:
import os
import boto3
def lambda_handler(events, context):
DYNAMODB_ENDPOINT_URL = os.environ.get("DYNAMODB_ENDPOINT_URL")
dynamodb = boto3.resource("dynamodb", endpoint_url=DYNAMODB_ENDPOINT_URL)
readings_table = dynamodb.Table(DYNAMODB_READINGS_TABLE_NAME)
readings_table.put_item(Item={"reading_id": "10", "other": "test"})
But I'm getting error: [ERROR] EndpointConnectionError: Could not connect to the endpoint URL: "http://localstack:4569/"
I've tried combinations of localhost and localstack along with ports: 4566 and 4569. All of them fail.
Here's my docker-compse service that I use to start localstack
localstack:
image: localstack/localstack:0.11.2
ports:
- 4566:4566
- 8080:8080
environment:
SERVICES: "dynamodb,sqs,lambda,iam"
DATA_DIR: "/tmp/localstack/data"
PORT_WEB_UI: "8080"
LOCALSTACK_HOSTNAME: localstack
LAMBDA_EXECUTOR: docker
AWS_ACCESS_KEY_ID: "test"
AWS_SECRET_ACCESS_KEY: "test"
AWS_DEFAULT_REGION: "us-east-1"
volumes:
- localstack_volume:/tmp/localstack/data
- /var/run/docker.sock:/var/run/docker.sock
# When a container is started for the first time, it will execute files with extensions .sh that are found in /docker-entrypoint-initaws.d.
# Files will be executed in alphabetical order. You can easily create aws resources on localstack using `awslocal` (or `aws`) cli tool in the initialization scripts.
# source: https://github.com/localstack/localstack/pull/1018/files#diff-04c6e90faac2675aa89e2176d2eec7d8R185
- ./localstack-startup-scripts/:/docker-entrypoint-initaws.d/
What would be the correct endpoint url that I have to set inside in my lambda so that I can send requests to localstack's DynamoDB?

Answer 1

According to the docs LOCALSTACK_HOSTNAME is a read-only env var:
LOCALSTACK_HOSTNAME: Name of the host where LocalStack services are available. Use this hostname as endpoint (e.g., http://${LOCALSTACK_HOSTNAME}:4566) in order to access the services from within your Lambda functions (e.g., to store an item to DynamoDB or S3 from a Lambda).

Answer 2

try with
ports:
- "0.0.0.0:4566-4599:4566-4599"
Hope it helps

Answer 3

By following Robert Taylor's answer, I was able to get the following working in my Java Lambda (this should really be a comment in that answer, but code formatting for big snippet is not adequate in comment, so I'm sharing this as a separate answer to make people's life easier):
var url = System.getenv("LOCALSTACK_HOSTNAME");
var credentials = new BasicAWSCredentials("mock_access_key", "mock_secret_key");
var ep = new AwsClientBuilder.EndpointConfiguration(String.format("http://%s:4566",url), "us-east-1");
s3 = AmazonS3ClientBuilder.standard()
.withEndpointConfiguration(ep)
.withPathStyleAccessEnabled(true)
.withCredentials(new AWSStaticCredentialsProvider(credentials))
.build();
dynamoDBMapper = new DynamoDBMapper(
AmazonDynamoDBClientBuilder.standard()
.withEndpointConfiguration(ep)
.withCredentials(new AWSStaticCredentialsProvider(credentials))
.build()
);